Nontarnishing rubber product and method of making the same



Patented Jan. 25, 1944 UNITED STATES c 2,340,233 NONTARNISHING RUBBER PBOQU 'J; AND I METHOD OF MAKING THE SAME Andrew Szegvari, Fairlawn, Olii'o, assig-iior to tion of Delaware American Anodelnc Akron, Ohio, a corpora- No Drawing-l Applicatiori' Novembe'r 1, 1939",

' Serial N 0. 302,363

. 4. Claims. (01. 260 8-21)' and rubber-like materials so as to' remove or render inert any sulfur materials on or near the surface or the rubber.

The sulfur materials including elemental sulfur and sulfur-containing compounds that are loundin vulcanized. rubber as well as in certain synthetic rubbers are prone to attack any susceptible obJect with which the rubber comes into contact. This is particularly noticeable in the tarnishing of silverware when it is cleaned in a rubber-lined dish washing machine. Other examples are when such susceptible materials are stored in a rubber-lined storage chest or on rubber-covered shelves. When rubber is bonded to metal, the metal itself is very often attacked by sulfur present in the vulcanized rubber. For convenience, all such deleterious eilects will be herein termed tarnishing effects.

1 have discovered a method of treating solid rubber as distinguished from rubber in any liquid form and particularly rubber coaguluhi that has been deposited from aqueous dispersionswhereby sulrur materials in the rubber are rendered inert with the result that objects normally subject to attack by the sulfur may be placed in close contact with the finished rubber and still be unaffected. In a preferred embodiment, a completely coagulated deposit of rubber coagulum containing suli'ur material is produced by coagulating a compounded aqueous dispersion of rubher in any well known manner, and the coagulated deposit is treated, while still in a, substantially undried water-containing condition, with an aqueous solution of a water-soluble compound of one of the inorganic metallic elements of Groups II and III of the generally followed qualitative analysis scheme or Treadwell and Hall. (F. P. Treadwell and W. T. Hall Analytical Chemistry, vol. I; eighth English edition; pages 133 and 207; published in 1932 by John Wiley and Sons, New York.) For example, the bath may be a solution of zinc ammonium chloride in dilute ammonium hydroxide, in which case zinc sulfide will be precipitated out. This treatment serves either to precipitate the sulfur or to render it inert in the sense of rendering it incapable of deleteriously affecting other objects, but the treatment does not interfere with the vulcanizing action of the sulfur.

As examples of the treating baths that may be used in this invention I have found that the iollowing will give excellent results: A solution or lead nitrate in water; a sblutioriof bismuth acetate iii dilute" scene id; a' solution or cupr c nitrate, sulfate or' chlori e in" water; a1 solution of cadmiumnitfate, su'li'ateor' ch ori e n water; a sbl ution of zinc l'iy e in dilute" potassium hydr i'clc'; asoiutionor zinc ammoniumchloride in dilute" ammonium hydroxide; a'solutioii' of tion ofnickel 'nydroxideir'i ammonium hydro'x e; a solution of st'annous' chloride in dfli'it' hydrochloric acid; a solution or nickel ammonium hypound in the treating bath is essential to the invention and widely varying concentrations may be used with satisiaction. Most of the metallic compounds employed are soluble only to a limited degree and it will accordingly be convenient for ordinary Iactory operations to utilize solutions which are substantially saturated with the metalllc compound. Such solutions are readily prepared and may be reproduced from time to time by ordinary workmen without expert supervision.

As a. pi-eierreu embodiment oi this invention, a rubber deposit is ionneo. irom latex that has been compounded with the usual vulcanizing agents including suliur, fillers, accelerators, ageresistors, coloring agents and the like. This deposited rubber, while it is still wet, is then immersed in a solution Ol' zinc ammonium chloride in weak ammonium hydroxide for five minutes. it is then withdrawn, washed and vulcahized by heating in the usual manner. By this treatment the sulfur and suiiur-containing compounds on or near the surface 01' the deposited rubber are rendered inert and are thereby incapable of attacking any susceptible obJect which may contact the rubber.

Rubber that has been deposited from aqueous dispersions is particularly adaptable for treatment by this invention because such deposited rubber, when freshly deposited, contains considerable amounts of water that is present in a continuous phase throughout the mass or deposited rubber. As the compounds that are used for preparing the solution employed as baths in this invention are water soluble they can penetrate the rubber by means of this continuous water phase and more effectively reach the sulfur in the interior of the mass. However, it has been found that this invention is also applicable for treating sulfur-containing compounded dry rubber that rubing sulfur or sulfur-compounds, as employed by those skilled in the art.

Having herein described preferred" embodithe appended claims.

I claim: 1. A method of making a non tarnishing rubber product which comprisespreparing a Isolidf" f" rubber composition having a continuous'water phase and containing sulfur material, and treat ing the composition with an aqueous solution of fawater-solublezinc salt, the treatment with zinc 'saltj'being effected while thecontinuous Water phase 'is'present in the rubber composition.

"2. 'A' method of producing a; non-tarnishing frubber pro'du'ct'which comprises coagulating rubbi' from fa""c'ompound'ed' aqueous dispersion of "'r'ubber containingsuliur material to produce a rubber coagul'um containing sulfur material and a" continuous waterphase and, while the consaid complex zinc salt.

tinuous water phase is present, treating the coagulum with a solution of a water-soluble complex zinc salt.

3. A method of producing a non-tamishing rubber product which comprises coagulating rubber from a-compounded aqueous dispersion of rubber containing sulfur material to produce a rubber coagulum containing sulfur material and a continuous water phase and, while the continuous water phase is present, treating the co- 'agulum' with a liquid composition comprising ments of my invention it is my wish to 'protect'it b a y limited only y he spi it n scopeof zine ammonium chloride in a dilute aqueous solutignof ammonium hydroxide. .lkAn article of manufacture, such as a dishwashingmachine, having a rubber portion which in normal use comes in contact with articles, such' as articles of silverware, which are tarnished or otherwise damaged by cont-act with sulfur materials, such as sulfur or sulfur-containing compounds, ordinarily present in rubber, said rubber product including su'ch sulfur material present as a non-tarnishing compound comprising the reaction product of the sulfur material with awater-soluble complex zinc salt, s-aidrubbe r product being prepared by treating the rubber while in a coagulated but undried, water containing condition with an aqueous solution of the I ANDREW SZEGVARI. 

